In recent years, more and more electronic devices are utilizing a capacitive switch or touch sensor as the premier form of user interface that facilitates the interaction between the user and the electronic device. Touch sensors are typically in the form of touch sensor pad, touch sensor sliders, touch sensor buttons, or touch sensor displays that operate by way of capacitive sensing.
In order to interact with the electronic device, the touch sensor detects a conductive object, such as a user's finger, by detecting a value corresponding to the human body's capacitance. The touch sensor detects a change in the electrostatic capacity and determines the presence or absence of contact (i.e., activation of the touch sensor) by comparing the detected value with a threshold value. If the detected value exceeds the threshold value the touch sensor is activated, and if the detected value is below the threshold value the touch sensor is not activated.
However, due to the widespread use of touch sensor devices in various different applications, the touch sensor device is often exposed to the elements. Typically in colder climates, users often wear hand covering such as gloves, mittens, or other apparel which protects the user's fingers from frigid temperatures. A disadvantage of the touch sensors is that the touch sensors are calibrated so as to have a specific sensitivity level in order to determine the presence or absence of the conductive object while avoiding the occurrence of misdetection. In order to provide a balance between misdetection and allow for accurate performance, the threshold of the touch sensor device is set so as to activate upon contact with an ungloved or bare human finger.
As such, users dealing with touch sensor devices which are exposed to colder temperatures such as electronic devices or kiosks positioned outside or unheated automotive vehicles exposed to the elements, are required to remove hand covering (i.e. gloves) prior to interaction with the touch sensor device. However, as the touch sensor device is itself exposed to the elements, removal of the hand covers is a major inconvenience for the user as it exposes the user's fingers to the frigid temperature in order for the user's bare finger to interact with the touch sensing device. If the user does not remove the hand covers prior to interaction with the touch sensing device, the hand covering acts as an insulator between the touch sensor and the user's finger thereby significantly decreasing the body capacitance able to be sensed by the touch sensor. As the touch sensor has been calibrated to actuate upon contact of a bare human finger, the contact of the insulated finger does not register and the touch sensor device is not activated.
With reference to FIG. 7, the operation of a previously known touch sensor operation will be discussed. FIG. 7 illustrates the relationship of the detected value D of the touch sensor and the predetermined threshold T during periods of no contact, contact with a insulated conductive object (such as a user wearing hand covers as seen in FIG. 3), and contact with a conductive object (such as a bare user's finger as seen in FIG. 2). The previously known touch sensor optionally includes a base value B representing a value from which the detected value D and the predetermined threshold T are measured in raw counts (i.e. the greater the capacitance the greater the raw counts). It is appreciated of course that the base value B is optionally set at zero or is an average self capacitance of the touch sensor. In the following explanation the base value B is set to zero (B=0).
The previously known touch sensor of FIG. 7 is provided with a constant predetermined threshold T=100 (having a threshold value of TV=100), and activation of the touch sensor occurs when the detected value D exceeds the predetermined threshold T=100. At time t0 to t1, there is no contact with a conductive object to the touch sensor, and the detected value D=25 which represents the self capacitance of the touch sensor and any environmental effect of the touch sensor which will be described in greater detail below. At time t1 to t2, a conductive object representing an insulated finger (FIG. 3) contacts the touch sensor. As the hand cover acts as an insulator to the body capacitance of the conductive object, the detected value is D1=75 which is less than the predetermined threshold T=100. Accordingly, the touch sensor remains in an OFF state even though the user's finger (insulating by the hand covering) is contacting the touch sensor. In time t2 to t3, no contact is made with the touch sensor. At time t3 to time t4, a conductive object in the form of a bare hand (FIG. 2) contacts the touch sensor, and the detected value is D2=135 which exceeds the threshold T=100. Therefore, the touch sensor is switched to an ON state.
As the self capacitance of the touch sensor increases or decreases directly with the increase or decrease in the temperature or humidity of the environment of the touch sensor, it is known to provide touch sensors that compensate for such an environmental effect. The previously known touch sensors vary either the base value (US Patent Application Publication No. 2008/0047764 to Lee et al.) or the threshold value (U.S. Patent Application Publication No. 2010/0258361 to Yamauchi et al.) to compensate for the change in the detected value due to the environment effects of temperature or humidity. Further, the change in the base value or the threshold value is based on the change in the temperature or humidity and are used to continuously calibrate the touch sensor so as to continuously compensate for variations in temperature and humidity. The previously known touch sensors utilize temperature or humidity sensors or calculated the compensation value due to the change in detected value over time.
The compensation for the environmental effects avoids the occurrence of an increase in the detected value due to an increase in temperature such that the detected value exceeds the threshold value even in the absence of user contact with the touch sensor, or the decrease in the detected value due to the decrease in temperature such that the detected value does not exceed the threshold value even in the presence of user contact with the touch sensor. However in the previously known environmental effect compensating touch sensors the difference between the threshold value and the base value is calibrated for detecting contact with a user's bare finger rather than the insulated user's finger due to the user wearing hand covers. As seen in FIG. 8, the relationship of the detected value D of the touch sensor and the compensated threshold T during periods of no contact, contact with a insulated conductive object (such as a user wearing hand covers as seen in FIG. 3), and contact with a conductive object (such as a bare user's finger as seen in FIG. 2). In this example the base value B is initially set to twenty (B=20).
The previously known environmental effect compensating touch sensor of FIG. 8 is provided with an initial threshold T=100. At time t0 there is no contact with a conductive object to the touch sensor, and the detected value D=25. From time t0 to t1, the environment of the touch sensor undergoes a decrease in temperature (from 60° F. to 35° F.) which decreases the detected value from D=25 to D=5, and the touch sensor compensates by reducing the threshold from T=100 to T=80. Although, the previously known compensating touch sensors vary the threshold, the threshold value TV between the base line and the threshold is held constant at TV=80. Accordingly, the amount the threshold is compensated is directly related to the environmental effect on the touch sensor (i.e. the change in detected value due to the change in temperature and humidity).
At time t1 to t2, a conductive object representing an insulated finger (FIG. 3) contacts the touch sensor. As the hand cover acts as an insulator to the body capacitance of the conductive object, the detected value is D1=50 which is less than the predetermined threshold T=80. Accordingly, the touch sensor remains in an OFF state even with the touch sensor's compensation for the environmental effect and the user's finger (insulating by the hand covering) is contacting the touch sensor. In time t2 to t3, no contact is made with the touch sensor. At time t3 to time t4, a conductive object in the form of a bare hand (FIG. 2) contacts the touch sensor, and the detected value is D2=90 which exceeds the compensated threshold value T=80. Therefore, the touch sensor is switched to an ON state.
However, as the threshold value TV is held constant, a user wearing a hand cover will be unable to actuate the touch sensor device without removing the hand cover as the relative sensitivity level of the previously noted touch sensor devices remains constant. Specifically, although the threshold or baseline value has been adjusted, that adjustment corresponds to the touch sensor's increase or decrease in self-capacitance corresponding to the environmental effect on the touch sensor. Therefore, a user will be required to remove the hand covering prior to interacting with the touch sensor.
Thus, there exists a need in the art to provide a touch sensing device which is capable of selecting a sensitivity level thereby allowing activation of the touch sensor by a user wearing hand covers.